The low-peel pressure sensitive adhesives available in commerce today have a high reject rate. They are highly compounded rubber compositions which contain large amounts of solvent, ranging up to about 60%, which must be removed before final curing of the adhesive takes place. Hot melt adhesives are also available, however, they have the disadvantage of a narrow utility range, i.e., the physical parameters must be adjusted and closely monitored for the hot melts to be in a useable condition.
To overcome these and other disadvantages of the above-mentioned adhesives, polyurethane-based adhesives have been proposed which are prepared by reacting a hydroxyl-containing liquid polymer with a prepolymer of an isocyanate-terminated polyester or polyether. Since the current coating apparatus can apply adhesives having viscosity of up to about 20,000 cps, efforts have been made to reduce viscosity of the polyurethane-based adhesives.